Balanced antenna feed



Aug. 21, 1956 H. J. RIBLET 2,760,193

BALANCEDANTENNA FEED Filed April 10, 1946 FIG.|

INVENTOR HENRY J. RIBLET ATTORNEY f ce i I Patented Aug. 21, 1956 BALANCED A TENNA FEED Henry J. Riblet, Erie, Pa., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application April 10, 1946, Serial N0. 660,868

6 Claims. or. 343-821) This invention relates to an antenna feed and more particularly to a balanced antenna feed to eliminate current from the transmission line as well as from the dipole.

The radiation patterns from these two radiators then combine to give an unexpected and usually undesirable resultant pattern.

Heretofore an antenna choke has been used to decouple the dipole from the outside of the outer conductor and reduce the current flow along the latter. The antenna choke took the form of a quarter wavelength sleeve, of inside diameter considerably larger than the outside diameter of the outer conductor of the coaxial transmission line, placed over the transmission line near the dipole. The end of the sleeve furthest from the dipole was short circuited to the outside of the outer conductor. The open circuited end of the sleeve considered in connection with the outer conductor presented a theoretically infinite impedance to current flow on the outer conductor. An antenna choke of this type is not entirely effective, however, and some radiation still takes place from the transmission line to interfere with the desired radiation pattern.

Therefore, it is an object of this invention to provide an antenna feed which is capable of producing a radiation pattern substantially the same as the pattern produced by a single dipole.

It is a further object of this invention to provide such an antenna feed which will excite negligible current on the outer conductor of the coaxial transmission line associated with it.

These and other objects will become apparent upon consideration of the following description in conjunction with the accompanying drawing in which:

Fig. 1 is a sectional view of one embodiment of this invention taken in the plane of the radiating dipoles, and

Fig. 2 is a sectional view of the embodiment of Fig. 1 taken perpendicular to the plane of the dipoles.

The drawing discloses the inner conductor and the outer conductor 11 of the coaxial transmission line through which power is transmitted to the antenna feed. Two center fed half wavelength dipoles 12 are supported perpendicular to the plane of the coaxial transmission line from the outer conductor 11 thereof by quarter wavelength stubs 13 of open wire transmission line. The dipoles 12 are center fed by excitation feeders 14 extending through apertures 15 in outer conductor 11 of the coaxial transmission line. The excitation feeders 14 couple power out of the coaxial transmission line by means of coupling loops 16 which are so positioned in the space between the inner conductor 10 and outer conductor 11 of the coaxial transmission line that the magnetic field lines therein thread the loops in opposite directions. This is most clearly seen in Fig. 2. The poles of the half wave dipoles 12 are electrically separated and excitation feeders 14 connect to diametrically opposite poles.

A p 2 The half wave dipoles 12, since they are center fed, require supports which keep their two poles electrically separate. Quarter wavelength stubs 13 are electrically short circuited at one end and by the outer conductor 11 of the coaxial transmission line so that they present a theoretically infinite impedance at the other end and thereby provide the necessary insulating effect between the two poles of each ofxthe dipoles 12. The excitation feeders 14 areiexcited degrees out of phase since their coupling loops 16 arethreaded in opposite direction by the magnetic field lines inside of the coaxial transmission line. However, since these excitation feeders 14 connect to diametrically opopsitepoles of the dipoles 12, the latter are excited in phase. I Thus the dipoles 12 operate in parallel to give an antenna feed which radiates with substantially the same pattern as the simple dipole. However, since the currents in the excitation feeders 14 are 180 degrees out of phase, any currents which may be excited on the outside of outer conductor 11 of the coaxial transmission line by reason of these currents in excitation feeders 14 will also be 180 degrees out of phase. The resulting cancellation will eliminate all undesirable currents and their accompanying radiation from the outside of the coaxial transmission line.

,The drawing discloses dipoles;12 having a curvature which facilitates enclosing them with a small pressurized housing but which has negligible electrical effect.

This invention is to be limited only by the appended claims and in no way by the one embodiment disclosed on the accompanying drawing:

What is claimed is:

1. Means for eliminating currents on an antenna feed line comprising, two center fed half wavelength dipoles, means for supporting said dipoles in radial juxtaposition, said supporting means electrically isolating the poles thereof, and two excitation feeders coupled to said feed line in such a manner that the magnetic field lines in said feed line thread said feeders in opposite directions whereby the currents in said excitation feeders are 180 degrees out of phase, said excitation feeders being connected to diametrically opposite poles of said dipoles to excite said dipoles in phase.

2. Means for eliminating the currents on the outer conductor of a coaxial feed line associated with an antenna comprising, two center fed half wavelength dipoles located parallel to one another in a plane perpendicular to the plane of said associated feed line, two stub supports made up of a quarter wavelength section of open wire transmission line short circuited at said outer conductor of said associated feed line, each of said supports having one conductor thereof connected to one pole of each of said dipoles to electrically isolate said poles of said dipoles and two excitation feeders coupled to said feed line in such a manner that the magnetic field lines in said feed line thread said feeders in opposite directions whereby the currents in said excitation feeders are 180 degrees out of phase, said excitation feeders being connected to diametrically opposite poles of said dipoles to excite said dipoles in phase.

3. Means for eliminating the currents on the outer conductor of a coaxial feed line associated with an antenna comprising, two center fed half wavelength dipoles located parallel to one another in a plane perpendicular to the plane of said associated feed line, two stub supports made up of quarter wavelength sections of open wire transmission line short circuited at said outer conductor of said associated feed line, each of said stub supports having one conductor thereof connected to one pole of each of said dipoles to electrically isolate said poles of said dipoles, and two excitation feeders inductively coupled to said associated feed line by coupling loops in the magnetic field thereof, said coupling loops extending through an aperture in said outer conductor of said feed line and each being threaded in an oppositedirect-ion by said magnetic field to give currents said excitation feeders which are 180 degrees out of phase, said excitation feeders being Connected todiametrically opposite poles of said dipoles to excite said dipoles in phase.

-4. An antenna systemfor transferring energy at a single frequency comprising, a coaxial central feed'line having inner and outer conductors, four support arms disposed in radial juxtaposition about the periphery of said outer conductor, said support arms being'integral therewith and extending substantially radially'theref-rorn for a distance equal to a quarter wave length *of said energy at said single frequency, a pair-of dipole radiators mounted on said support arms such that the separate poles thereof are each connected to said outer conductor by one of said four support arms, a pair of couplingloops inserted 'within said outer conductor and oriented such that said loops are threaded in opposite directions by'the magnetic field lines in said feed line whereby currents induced therein are 180 out of phase, and-separate'probes extending from each of said coupling loops to alternate poles of said dipole radiators, said probes passing between pairs of said support arms.

'5. Apparatus as in claim 4 wherein said dipole radiators are arcuate in shape forming a portion of a common circle.

6. In combination, a coaxial feed line having inner and outer conductors, 'two center-fed half wave length dipoles located in a substantially colinear relationship on opposite sides of said outer conductor in aplane perpendicular to the longitudinal axis of said coaxial feed line, said dipoles being supported away from said outer conductor by stub supports consisting of a quarter wave length section of open wire transmission line short-circuited at said outer conductor, a first and second excitation feeder, said feeders being coupled at one end to said coaxial line via oppositely d-irected'inductive =loopsextending into the space between said inner and outer conductors whereby said loops are threaded in-opposite tdirections bythe magnetic field lines in said line whereby the currents in said feeders are out of phase, and means for reversely connecting the other end of said feeders to said dipoleswhereby the current flow therein is in the same spatial direction.

References Cited in the file of this patent UNITED STATES PATENTS 

